Device and method for generating piston outline machining data and computer-readable recording medium on which machining data generation program is recorded

ABSTRACT

A machining data generator generates NC machining data specifying machining operations for shaping the external shape of a piston. The machining data generator uses a machining data sheet (provided by a spreadsheet software) describing noncircular part shape data on the shape of a noncircular part and condition data (machining condition data and shape data on shapes of parts other than the noncircular part necessary for shaping the overall shape of the piston). The machining data sheet is prepared beforehand. A machining data generation program reads the machining data sheet in step S 4 , recognizes directives “start cell” and “end cell” defining a cell region and described in the machining data sheet and fetches matrix data from the cell region in step S 5 , and fetches condition data other than the noncircular part shape data from the machining data sheet, and calculates NC machining data to be given to a NC machine tool on the basis of the condition data and the noncircular part shape data in step S 6 . Data management work for individually managing the noncircular part shape data and the other condition data is not necessary, those data can be collectively managed, and the relevant data can be collectively entered.

TECHNICAL FIELD

The present invention relates to a NC machine tool for shaping aworkpiece in a piston and, more particularly, to a machining datagenerator for generating machining data to be given to a NC machinetool, the machining data specifying machining operations for machining aworkpiece in a desired external shape of a piston.

BACKGROUND ART

Referring to FIG. 9, a NC machine tool disclosed in JP-B 6-75814 formachining a workpiece W to shape a noncircular part, having an ellipticor noncircular cross section, of a piston holds the workpiece W on thespindle that rotates about an axis C, rotates the spindle, minutelycontrols the movement, for radial feed in directions along the Y-axis,of a tool H held on a tool holder of the NC machine tool in synchronismwith the rotation of the spindle and moves the tool H for longitudinalfeed in directions along the Z-axis.

The surface shape of the noncircular part of the piston is specified bymatrix data designating the position of a point by a distance from theorigin on the axis C of the spindle, namely, the Z axis, an angle aboutthe axis C, and a radial distance on the Y-axis.

As shown in FIG. 9, a piston formed by machining the workpiece W has aland part A provided with ring grooves for receiving piston rings and askirt part B continuous with the land A. A noncircular part having anoncircular cross section is included, in most cases, in the skirt partB. The edge of the skirt part B in directions along the Z axis, namely,the profile, is irregular. A NC machining data generator for generatingmachining data for controlling NC machining for forming such a surfaceshape is proposed in JP-A 7-319528.

The machining data generator mentioned in JP-A 7-319528 generates axialshape data and radial shape data by from numerical data specifying apolygon, and generates NC machining data by combining the axial shapedata and the radial shape data. Shape data for controlling machining toform the noncircular part is given directly to the NC machining datagenerator by a keyboard, and data specifying machining conditionsincluding the rotating speed of the workpiece about the axis C andlongitudinal feed along the Z-axis for forming the noncircular part isgiven directly to the NC machining data generator by a keyboard.

The shape data and the machining data on machining conditions need to begiven separately to the prior art machining data generator mentioned inJP-A 7-319528. Therefore, those data must be individually managed andrequire troublesome management work.

As mentioned above, the piston has the cylindrical land part A havingthe circular part with a circular cross section, and the skirt part Bhaving the noncircular part with a noncircular cross section. An actualturning operation forms the land part A continuously with the skirt partB. Shape data needed for machining the land part A is given separatelyto the prior art machining data generator. Thus, those data are givenseparately by separate data input operations. When the data inputoperations are performed separately, errors are liable to be made inentering data, and entering or loading the same data again into themachining data generator is a very time-consuming job.

It is an object of the present invention to provide a machining datagenerator for generating machining data for shaping a piston by NCmachining, capable of previously collecting shape data on a noncircularpart of the piston, namely, matrix data, and other condition datanecessary for forming the general external shape of the piston, such asmachining condition data and additional shape data on parts other thanthe noncircular part, in a single machining data sheet, to saveindividually managing various data and to enter the relevant datacollectively.

Another object of the present invention is to provide a machining datagenerator for generating machining data for shaping a piston by NCmachining, capable of easily examining the appropriateness of shape dataon a noncircular part of the piston and of intuitively correcting shapedata on the noncircular part.

A third object of the present invention is to provide a machining datagenerator for generating machining data for shaping a piston by NCmachining, capable of easily examining the appropriateness of generatedNC machining data.

DISCLOSURE OF THE INVENTION

A machining data generator in a first aspect of the present inventionfor generating machining data for shaping an external shape of a pistonincludes: a noncircular part shape data fetching unit that reads amachining data sheet in which both noncircular part shape data formachining a noncircular part having a noncircular cross section of thepiston and machining condition data are described and that fetches thenoncircular part shape data from the machining data sheet; and a NCmachining data calculating unit that recognizes the machining conditiondata described in the machining data sheet and that calculates NCmachining data on the basis of the recognized machining condition dataand the noncircular part shape data fetched by the noncircular partshape data fetching unit. Since the machining condition data isdescribed together with the noncircular part shape data on the singlemachining data sheet, the data can be easily managed and all the datanecessary for machining can be collectively obtained by reading themachining data sheet. Consequently, errors will not be made in enteringdata, and operations for entering the same data again and reloading thesame data can be saved.

In the machining data generator in the first aspect of the presentinvention, it is preferable that additional shape data on a part otherthan the noncircular part is described in the machining data sheet, andthe NC machining data calculating unit recognizes the additional shapedata described in the machining data sheet together with the machiningcondition data and calculates NC machining data on the basis of therecognized machining condition data and the additional shape data, andthe noncircular part shape data fetched by the noncircular part shapedata fetching unit. Since the additional shape data, including the landpart shape data, other than the noncircular part shape data is describedtogether with the noncircular part shape data on the single machiningdata sheet, the data can be easily managed and all the data necessaryfor shaping the overall external shape of the piston can be collectivelyentered.

In the machining data generator in the first aspect of the presentinvention, it is preferable that the machining data sheet is a sheetprovided by a spreadsheet software and the noncircular part shape datais described in the sheet of the spreadsheet software in a form ofmatrix data indicating coordinates for machining and arranged in rowsand columns. Since the sheet provided by the general spreadsheetsoftware is used as the machining data sheet for describing thenoncircular part shape data, the noncircular part shape data can beeasily produced and managed.

In the machining data generator in the first aspect of the presentinvention, it is preferable that the noncircular part shape data defineseach of positions by an axial coordinate on the axis of a workpiece (apoint on a Z-axis), an angular coordinate (an angle about a C-axis) anda radial coordinate (a point on a Y-axis), and the noncircular partshape data is described in the sheet of the spreadsheet software in aform of matrix data represented by axial coordinates and angularcoordinates arranged in rows and columns. Since the noncircular partshape data defined by the axial coordinates, the angular coordinates andthe radial coordinates is described in the matrix data represented bythe axial coordinates and the angular coordinates arranged in rows andcolumns, the noncircular part shape data can be more easily and surelyproduced and managed and can be more easily and surely converted intothe NC machining data.

In the machining data generator in the first aspect of the presentinvention, it is preferable that shape-data-describing-area-specifyingdata that specifies a cell region in which the matrix data is entered isdescribed in the machining data sheet, and the noncircular part shapedata fetching unit recognizes the cell region specified by theshape-data-describing-area-specifying data when the noncircular partshape data fetching unit reads the machining data sheet to fetch thenoncircular part shape data from the cell region. Since the cell regionspecified by the shape-data-describing-area-specifying data isrecognized and the noncircular part shape data entered in the recognizedcell region is fetched, the noncircular part shape data arranged in thesheet of the spreadsheet software and other condition data can be readseparately and the wrong application of the data can be effectivelyprevented.

It is preferable that the machining data generator in the first aspectof the present invention further includes a graphic display unit thatgraphically displays the noncircular part shape data. The graphicdisplay unit facilitates the visual recognition of the shape of thenoncircular part represented by the noncircular part shape data andhence the appropriateness of the noncircular part shape data can beeasily examined.

Preferably, the graphic display unit includes an enlarging unit thatdisplays a part of the graphically displayed noncircular part shape datain an enlarged picture. Thus, details of the shape of the noncircularpart represented by the noncircular part shape data can be visually andprecisely recognized and the appropriateness of the noncircular partshape data can be easily examined.

Preferably, the graphic display unit has a correcting unit that correctsthe graphically displayed noncircular part shape data on a graphicdisplay screen. Since the noncircular part shape data can be correctedby modifying a picture displayed on the graphic display screen withoutentering numerals, the noncircular part shape data can be intuitivelycorrected.

Preferably, the graphic display unit has a tolerance data display unitthat graphically displays tolerance data on tolerances for thenoncircular part shape data together with the noncircular part shapedata. Since it is possible to visually verify whether or not differencesof the corrected noncircular part shape data from reference noncircularpart shape data are within the tolerances, the appropriateness of thecorrected noncircular part shape data can be easily examined.

The machining data generator in the first aspect of the presentinvention may further include a simulation display unit that graphicallydisplays a machining position (a position on the Y-axis and the like)and a machining speed (speed along the Y-axis) on a time axis as areference axis on the basis of the NC machining data calculated by theNC machining data calculating unit. Thus, the appropriateness ofmachining positions (positions on the Y-axis and the like) and machiningspeed (speed along the Y-axis) from the start to the end of machiningcan be easily verified.

Preferably, the simulation display unit indicates a time indication linethat moves along the time axis on the graphic display screen displayingthe machining positions (positions on the Y-axis and the like) and themachining speed (speed along the y-axis), and displays information aboutthe rotation of the spindle about the C-axis at a position indicated bythe time indication line. Since the rotation information about thevariation of the rotation of the spindle about the C-axis, the machiningposition (position on the Y-axis and the like) and the machining speed(speed along the Y-axis) with time from the start of machining, can berecognized on the graphic display screen, the appropriateness of thosedata can be easily verified.

A machining data generating method of generating machining data forshaping an external shape of a piston in a second aspect of the presentinvention includes: preparing a machining data sheet describingnoncircular part shape data specifying machining operations formachining a noncircular part having a noncircular cross section of thepiston together with machining condition data; reading the machiningdata sheet and fetching the noncircular part shape data from themachining data sheet; and recognizing the machining condition datadescribed in the machining data sheet and calculating NC machining dataon the basis of the recognized machining condition data and the fetchednoncircular part shape data.

In the machining data generating method in the second aspect of thepresent invention, it is preferable that additional shape data on a partother than the noncircular part is described additionally in themachining data sheet, the additional shape data described in themachining data sheet is recognized together with the machining conditiondata, and the NC machining data is calculated on the basis of therecognized machining condition data and additional shape data, and thefetched noncircular part shape data.

A machining data generation program in a third aspect of the presentinvention specifying machining operations for shaping an external shapeof a piston makes a computer execute: a procedure for reading amachining data sheet describing noncircular part shape data formachining a noncircular part having a noncircular cross section of thepiston together with machining condition data and for fetching thenoncircular part shape data from the machining data sheet; and aprocedure for recognizing the machining condition data described in themachining data sheet and calculating NC machining data on the basis ofthe recognized machining condition data and the fetched noncircular partshape data. The machining data generation program may be recorded in acomputer-readable recording medium from which a computer is able to readrecorded information.

In the machining data generation program in the third aspect of thepresent invention, it is preferable that additional shape data on a partother than the noncircular part is described further in the machiningdata sheet, and the machining data generation program further executes aprocedure for recognizing the additional shape data described in themachining data sheet, and calculating NC machining data on the basis ofthe recognized machining condition data and additional shape data, andthe fetched noncircular part shape data.

In the machining data generating method in the second aspect of thepresent invention and the machining data generation program in the thirdaspect of the present invention, the machining condition data isdescribed in combination with the noncircular part shape data in thesingle machining data sheet. Therefore, the data can be easily managedand various data can be collectively entered by reading the machiningdata sheet. Since the other shape data (shape data on the land part andthe like) is described in addition to the machining condition datatogether with the noncircular part shape data in the single machiningdata sheet, the data can be easily managed and all the data necessaryfor shaping the overall external shape of the piston can be collectivelyentered.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a machining data generator in apreferred embodiment of the present invention for generating machiningdata specifying machining operations for shaping the external shape of apiston;

FIG. 2 is an example of a machining data sheet to be used by themachining data generator shown in FIG. 1;

FIG. 3 is a flow chart of procedures of a NC data producing programrealizing the machining data generator shown in FIG. 1;

FIG. 4 is view of an example of a graphic display screen graphicallydisplaying a noncircular part shape data;

FIG. 5 is a view of the graphic display screen graphically displaying apart of the noncircular part shape data shown in FIG. 4 in an enlargedpicture;

FIG. 6 is a view of a graphic display screen (simulation screen)displaying an example of a picture showing the result of simulation(positions on the Y-axis and speeds along the Y-axis) on time axes asreference axes;

FIG. 7 is a view of the graphic display screen (simulation screen)displaying an example of a picture showing a part of the result ofsimulation on expanded time axes;

FIG. 8 is a view of a computer as hardware for realizing the machiningdata generator shown in FIG. 1; and

FIG. 9 is a schematic sectional view of an example of a piston to beformed by machining on the basis of NC machining data generated by themachining data generator shown in FIG. 1.

BEST MODE FOR CARRYING OUT THE INVENTION

A machining data generator in a preferred embodiment of the presentinvention for generating machining data for shaping the external shapeof a piston will be described with reference to FIGS. 1 to 9.

Referring to FIG. 1, a machining data generator 20 in a preferredembodiment of the present invention has a noncircular part shape datafetching unit 21, a NC machining data calculating unit 22, a graphicdisplay unit 23 and a simulation display unit 24.

Operations of the machining data generator 20 shown in FIG. 1 arecarried out by executing a NC machining data generation program by acomputer 6 shown in FIG. 8. The computer 6 shown in FIG. 8 has a CPU 1,an internal memory device 2, a keyboard 3, a CRT 4 and an externalstorage device 5. The NC machining data generation program is stored inthe internal memory device 2. The CPU 1 of the computer 6 reads andexecutes sequentially instructions specified in the NC machining datageneration program stored in the internal storage device 2 to carry outthe following various functions. The NC machining data generationprogram may be stored in a computer-readable recording medium, such as aflexible disk or a CD-ROM.

The noncircular part shape data fetching unit 21 of the machining datagenerator 20 shown in FIG. 1 reads a machining data sheet 10 and fetchesnoncircular part shape data from the machining data sheet 10. The NCmachining data calculating unit 22 recognizes other condition data otherthan the noncircular part shape data, namely, machining condition dataand shape data on shapes of parts other than a noncircular partnecessary for shaping the overall external shape of a piston, describedin the machining data sheet 10. The NC machining data calculating unit22 calculates NC machining data on the basis of the recognized othercondition data (machining condition data and shape data on shapes ofparts other than the noncircular part) and the noncircular part shapedata fetched by the noncircular part shape data fetching unit 21. Thegraphic display unit 23 displays the noncircular part shape datagraphically. The simulation display unit 24 displays machining positionsand machining speeds on time axes as reference axes graphically.

The machining data sheet 10 is a sheet of a spreadsheet software made inadvance, as shown in FIG. 2. The spreadsheet software is, for example,Excell® (Microsoft). The noncircular part shape data specifyingconditions for shaping a noncircular part having a noncircular crosssection is described in a cell region 11 of the machining data sheet 10.

The noncircular part of the piston is, for example, a skirt part B shownin FIG. 9. As shown in FIG. 4, the external shape of the noncircularpart is described by radial decrements of points from the radius of areference circle RS, at fixed angular intervals of 5° on the outlines ofcross sections taken on planes at fixed axial pitches of 1 mm along theZ-axis parallel to the height of a workpiece W. The height of the skirtpart B is 40 mm by way of example.

In the machining data sheet 10 shown in FIG. 2, angles θ_(i) about theC-axis are arranged in rows, and positions Z_(n) on the Z-axis arearranged in columns. Radial data R (Z_(n), θ_(i)) are entered in cellsat the intersections of the rows and the columns, respectively, inmatrix data. Since the cross section of the noncircular part of thepiston is symmetrical with respect to a center line as shown in FIG. 4,only the data on the points at angular positions between 0° and 180° isdescribed.

The machining data sheet 10 has a head part including cells A2 and A3named “start cell” and “end cell” as directives, respectively. Cellposition data indicating the cell region 11, namely,shape-data-describing-area-specifying data, is entered in cells B2 andB3 adjacent to the cells A2 and A3. In the machining data sheet 10 shownin FIG. 2, “start position” is “C5” and “end position” is “K45”. Whenthe noncircular part shape data fetching unit 21 reads the machiningdata sheet 10, the noncircular part shape data fetching unit 21recognizes the cell region 11, namely, a region between “C5” and “K45”,specified by the cell position data(shape-data-describing-area-specifying data) described in the cells B2and B3, and fetches the noncircular part shape data (matrix data)arranged in the specified cell region 11.

Other condition data necessary for shaping the overall external shape ofthe piston including machining condition data specifying tolerances forsizes of the noncircular part, units of the numerical values of thematrix data and machining conditions necessary for generating NCmachining data, and shape data on shapes of parts other than thenoncircular part, such as the diameter of the land part A are describedafter directives indicating the contents of the data in the machiningdata sheet 10. More concretely, a directive “C-axis rotating speed”indicates rotating speed about the C-axis. A rotating speed r1 isdescribed in a cell on a row indicated by the directive “C-axis rotatingspeed”. Other machining conditions are described in a similar manner.

Thus, all the data necessary for shaping the overall external shape ofthe piston is described collectively in the single machining data sheet10. The machining data sheet 10 can be made in spare time. Thenoncircular part shape data and other condition data necessary formachining are held collectively in a single file. Thus, the data can beeasily managed as compared with individually managing those data, andthe various data necessary for machining can be collectively entered byreading the machining data sheet 10. Consequently, errors will not bemade in entering data, and operations for entering the same data againand reloading the same data can be saved.

A NC machining data generation program realizing the machining datagenerator 20 shown in FIG. 1 will be described with reference to FIG. 3.The NC machining data generation program includes three procedures,namely, a NC machining data generation procedure, a noncircular partshape data examination procedure and a NC machining data simulationprocedure. The steps of those procedures included in the NC machiningdata generating program 20 constitute functional means.

(NC Machining Data Generation Procedure)

The NC machining data generation procedure will be explained.

The NC machining data generation program has step S1 instructing the NCmachining data generator to start the NC machining data generationprocedure. Then, the previously prepared machining data sheet 10 is readfrom the external storage device 5 or the internal memory device 2 ofthe computer 6 in step S4.

In step S5, a shape-data-describing-area-specifying data described inthe machining data sheet 10 is recognized and the noncircular part shapedata (matrix data) is fetched from the cell region specified by theshape-data-describing-area-specifying data (noncircular part shape datafetching means). For example, suppose that the machining data sheet 10shown in FIG. 2 is given. Then, the directives “start cell” and “endcell” are recognized, and the noncircular part shape data (matrix data)arranged in the cell region 11 specified by the contents (“C5”, “K45”)of the cells B2 and B3 following the “start cell” and the “end cell” isread.

In step S6, directives specifying pieces of the condition data otherthan the noncircular part shape data are discriminated; numerical valuesgiven by the machining data sheet 10 are given to a NC machining dataconversion program describing those directives as parameters; and NCmachining data to be given to a NC machine tool is calculated on thebasis of the other condition data and the noncircular part shape dataobtained in step S5 (NC machining data calculating means).

The noncircular part shape data described in the machining data sheet 10specifies the radial data on points at axial pitches of 1 mm along theZ-axis and angular intervals of 5° about the C-axis. When those data areconverted into the NC machining data, machining conditions includinglongitudinal feed along the Z-axis and rotating speed about the C-axisare taken into consideration. Thus, the number of pieces of matrix datafor controlling NC machining is far greater than that of pieces of datadescribed in the machining data sheet 10. Naturally, data on points inthe angular range of 0° to 360° about the C-axis is calculated. Sinceshape data for shaping the land part A of the piston is read also,longitudinal position data specifying the longitudinal positions ofpoints with respect to the direction along the axis of the workpiece W,namely, the Z-axis, includes data specifying the positions of points inthe length of the land part A along the Z-axis.

In step 57 subsequent to step S6, the calculated NC machining data isstored in predetermined places in the internal memory device 2 of thecomputer 6 (data storage command means), and then the NC machining datais transferred to the NC machine tool in step S8 (data transfer means).

(Noncircular Part shape Data Examination Procedure)

The noncircular part shape data examination procedure will be explained.

The noncircular part shape data examination procedure has step S2instructing the NC machining data generator to start the noncircularpart shape data examination procedure. Operations similar to thoseexecuted in steps S4, S5 and S6 of the NC machining data generationprocedure are executed in steps S4, S5 and S6 following step S2.

In step S9 subsequent to step S6 of the noncircular part shape dataexamination procedure, the noncircular part shape data (matrix data)described in the machining data sheet 10 is displayed graphically on thescreen of the CRT 4 of the computer 6 (graphic display means). A picturespecified by the noncircular part shape data is displayed on the screenof the CRT 4 as shown in FIG. 4 in step S9. In FIG. 4, the externalshape (profile) BI of the entire noncircular part is displayed in aright half region of the screen of the CRT 4 of the computer 6, and across section of the external shape B1 in a plane at a specifiedposition on the Z-axis is displayed in a left half region of the screenof the CRT 4.

When the cross section displayed in the left half region of the screenis turned at angular intervals specified in the machining data sheet 10by operating the right move key and the left move key for moving thecursor of the keyboard 3 of the computer 6, the external shape B1displayed in the right half region of the screen turns accordingly andan updated external shape of a cross section in a plane including areference line L1 is displayed.

The Z-axis position on the Z axis of the cross section displayed in theleft half region of the screen can be moved along the Z-axis at a pitchspecified in the machining data sheet 10 and can be determined byoperating the up key and the down key of the keyboard 3. FIG. 4 shows ashape at a Z-axis position Zn of 40 mm and an angular position θ_(i) of0° about the X-axis.

A part of the noncircular part shape data graphically displayed on thescreen can be displayed in an enlarged picture. An instructionrequesting enlarging a desired rectangular area is given by specifying acorner of the rectangular area and another corner diagonally opposed tothe former corner by operating a mouse. then, a part of the noncircularpart shape data corresponding to the desired rectangular area can beenlarged in proportion to the size of the screen as shown in FIG. 5 instep S11 (picture enlarging means). Since the part of the noncircularpart shape data is graphically displayed in an enlarged picture, detailsof the shape of a part of the noncircular part specified by the selectedpart of the noncircular part shape data can be surely recognized throughvisual observation.

Tolerance data specifying tolerances for the noncircular part specifiedby the noncircular part shape data can be graphically displayed togetherwith the noncircular part shape data. When a tolerance displayinstruction is given by operating the keyboard 3 or the mouse in stepS12, short lines as tolerance marks 15 indicating tolerances for thenoncircular parts described in the machining data sheet 10 are displayedat predetermined angular pitches of, for example, 5° as shown in FIG. 5(tolerance data display means). When the noncircular part shape data iscorrected in steps S14 and S15, the graphical display of the tolerancedata for the noncircular part together with the noncircular part shapedata (sectional shape data) facilitates the visual verification ofwhether or not the differences of corrected noncircular part shape datafrom the reference noncircular part shape data are within thetolerances.

The noncircular part shape data graphically displayed on the screen canbe corrected by operating the pictures displayed on the screen. As shownin FIG. 5, a correction cursor 16 indicating a curve representing theprofile of a cross section is displayed on the reference line L1. Thecursor 16 can be vertically moved by operating two appropriate keys ofthe keyboard 3, such as a key A and a key S. When it is decided in stepS14 that the cursor 16 has been vertically moved, relevant data amongthe noncircular part shape data (matrix data) described in the machiningdata sheet 10 is corrected in step S15 (correcting means). The thuscorrected noncircular part shape data is stored in a machining datasheet of a file name different from that of the read machining datasheet 10 in step S16. Since the noncircular part shape data is correctedby operating the picture graphically displayed on the screen, theintuitive correction of the noncircular part shape data is possible.Since the part of the noncircular part shape data graphically displayedin an enlarged picture, details of the shape of the noncircular part canbe surely and visually recognized.

Although this noncircular part shape data examination procedurecalculates the NC machining data in step S6, the results of calculationdo not need necessarily to be used in steps S9 to S16.

(NC Machining Data Simulation Procedure)

The NC machining data simulation procedure will be explained.

The NC machining data generation program has step S3 instructing the NCmachining data generator to start the NC machining data simulationprocedure. Operations similar to those executed in steps S4, S5 and S6of the NC machining data generation procedure are executed in steps S4,S5 and S6 following step S3.

In step S17 subsequent to step S6 of the NC machining data simulationprocedure, the NC machining data calculated in step S6 is displayedgraphically on the screen of the CRT 4 of the computer 6 (simulationdisplay means).

The NC machining data is displayed graphically on the screen of the CRT4 in step S17 in a simulation picture as shown in FIG. 6 (simulationpicture). In the simulation picture shown in FIG. 6, time is measured ona horizontal time axis, and the machining position (radial position onthe Y-axis) of the tool H after a time elapsed after the start of amachining operation calculated on the basis of the longitudinal feedspeed in a direction parallel to the Z-axis and the speed andacceleration of the tool H with respect to a direction parallel to theY-axis are displayed graphically.

Also shown in the simulation picture are information about the rotationof the work W about the C-axis including the rotating speed of the workW about the C-axis during NC machining, an angle about the C-axis andthe number of turns of the work W after the start of the machiningoperation, the position of the tool H on the Z-axis and informationrelating with the Y-axis (the position on the Y-axis of the tool H withrespect to a datum point on the lathe, and incidental Y-axisinformation).

A vertical time indicating line T displayed on the screen can belaterally moved along the time axis by operating the right move key andthe left move key for controlling the cursor of the keyboard 3. Theposition of the time indicating line T on the time axis indicates timeelapsed after the start of machining. The elapsed time is displayed inan upper part of the screen, and information about the rotation of thework W about the C-axis and a position on the Z-axis at the end of theelapsed time displayed in the upper part of the screen is displayed in alower part of the screen.

In the simulation picture shown in FIG. 6, the time axis is compressedto display all the machining operations for producing a piston. In asimple section a indicating machining operations for forming the landpart A, the position of the tool H is on a fixed line fixed with respectto directions along the Y-axis, signifying that a machining operationsfor cylindrical turning is being performed. In a complicated section bindicating machining operation for forming the skirt part B, theposition of the tool H changes in opposite directions along the Y-axisat a high frequency, signifying that a machining operation fornoncircular turning is being performed.

A part of the simulation picture, similarly to the graphic picture shownin FIG. 4, can be displayed in an enlarged picture. FIG. 7 shows anenlarged picture illustrating a transient stage of machining where amachining operation for forming the land part A is completed and amachining operation for forming the skirt part B is started (enlargeddisplay means).

Thus, the appropriateness of the generated NC machining data(appropriateness of the movement of the tool with respect to the Y-axis)can be easily visually verified through the examination of thecalculated NC machining data calculated in step S6 and graphicallydisplayed on the screen in the simulation picture.

1. A machining data generator for generating machining data for shapingan external shape of a piston, said machining data generator comprising:a spreadsheet software unit that describes noncircular part shape datadefined by a longitudinal coordinate on an axis of a workpiece, anangular coordinate corresponding to the longitudinal coordinate, and aradial coordinate corresponding to the angular coordinate in a form ofmatrix data in a machining data sheet, and describesshape-data-describing-are-specifying data that specifies a cell regionin which the matrix data is entered, and machining condition data thatspecifies machining conditions for shaping the noncircular part of thepiston, after directives in the machining data sheet; a noncircular partshape data fetching unit that recognizes the cell region specified bythe shape-data-describing-area-specifying data in reading the machiningdata sheet and fetching the noncircular part shape data; and a NCmachining data calculating unit that recognizes the machining conditiondata described in the machining data sheet and that calculates NCmachining data on the basis of the recognized machining condition dataand the noncircular part shape data fetched by the noncircular partshape data fetching unit.
 2. The machining data generator according toclaim 1, wherein additional shape data on a part other than thenoncircular part is described in the machining data sheet, and the NCmachining data calculating unit recognizes the additional shape datadescribed in the machining data sheet together with the machiningcondition data and calculates NC machining data on the basis of therecognized machining condition data and the additional shape data, andthe noncircular part shape data fetched by the noncircular part shapedata fetching unit.
 3. (canceled)
 4. (canceled)
 5. (canceled)
 6. Themachining data generator according to claim 1, further comprising agraphic display unit that graphically displays the noncircular partshape data in a picture of a cross section of the noncircular part at aspecified axial position, and a picture of an outline of the noncircularpart cut along a reference longitudinal line in the picture of the crosssection, placed beside the picture of the cross section, wherein theaxial position of the cross section can be specified.
 7. The machiningdata generator according to claim 6, wherein the graphic display unitincludes an enlarging unit that displays a part of the graphicallydisplayed noncircular part shape data in an enlarged picture.
 8. Themachining data generator according to claim 6, wherein the graphicdisplay unit has a correcting unit that corrects the graphicallydisplayed noncircular part shape data on a graphic display screen. 9.The machining data generator according to claim 6, wherein the graphicdisplay unit has a tolerance data display unit that graphically displaystolerance data on tolerances for the noncircular part shape datatogether with the noncircular part shape data.
 10. The machining datagenerator according to claim 1, further comprising a simulation displayunit that graphically displays a machining position and a machiningspeed of a tool on a time axis as a reference axis on the basis of theNC machining data calculated by the NC machining data calculating unit.11. The machining data generator according to claim 10, wherein thesimulation display unit indicates a time indication line that movesalong the time axis on the graphic display screen displaying themachining position and machining speed of the tool, and displaysinformation about a rotation of the spindle at a position indicated bythe time indication line.
 12. A machining data generating method ofgenerating machining data for shaping an external shape of a piston,said method comprising: preparing a machining data sheet of aspreadsheet software for NC machining data calculation by describingnoncircular part shape data specifying a noncircular part of the pistonin a form of matrix data defined by a longitudinal coordinate on an axisof a workpiece, an angular coordinate corresponding to the longitudinalcoordinate and a radial coordinate corresponding to the angularcoordinate, and by describing shape-data-describing-area-specifying datathat specifies a cell region in which the matrix data is entered, andmachining condition data that specifies machining conditions for shapingthe noncircular part of the piston, after directives in the machiningdata sheet; recognizing the cell region specified by theshape-data-describing-area-specifying data when reading the machiningdata sheet and fetching the noncircular part shape data from the cellregion; and recognizing the machining condition data described in themachining data sheet and calculating NC machining data on the basis ofthe recognized machining condition data and the fetched noncircular partshape data.
 13. The machining data generating method according to claim12, wherein additional shape data on a part other than the noncircularpart is described additionally in the machining data sheet, theadditional shape data described in the machining data sheet isrecognized together with the machining condition data, and the NCmachining data is calculated on the basis of the recognized machiningcondition data and additional shape data, and the fetched noncircularpart shape data.
 14. A computer-readable recording medium storing amachining data generation program for generating machining data onmachining operations for shaping an external shape of a piston, to beexecuted by a computer, characterized in that the machining datagenerating program executes: a procedure for preparing a machining datasheet spreadsheet software for NC machining data calculation bydescribing noncircular part shape data specifying a noncircular part ofthe piston in a form of matrix data defined by a longitudinal coordinateon a axis of a workpiece, an angular coordinate corresponding to thelongitudinal coordinate and a radical coordinate corresponding to theangular coordinate, and by describingshape-data-describing-area-specifying data that specifies a cell regionin which the matrix data is entered, and machining condition data thatspecifies machining conditions for shaping the noncircular part of thepiston, after directives in the machining data sheet; a procedure forrecognizing the cell region specified by theshape-data-describing-area-specifying data when reading the machiningdata sheet and fetching the noncircular part shape data from the cellregion; and a procedure for recognizing the machining condition datadescribed in the machining data sheet and calculating NC machining dataon the basis of the recognized machining condition data and the fetchednoncircular part shape data.
 15. The recording medium according to claim14, wherein additional shape data on a part other than the noncircularpart is described in the machining data sheet, and the machining datagenerating program further executes a procedure for recognizing theadditional shape data described in the machining data sheet and themachining condition data and calculating NC machining data on the basisof the recognized machining condition data and additional shape data,and the fetched noncircular part shape data.
 16. The machining datagenerator according to claim 6, wherein the graphic display unit isadapted to turn a cross section of the noncircular part at a specifiedlongitudinal position at a predetermined angular interval.
 17. Themachining data generator according to claim 2, further comprising agraphic display unit that graphically displays the noncircular partshape data in a picture of a cross section of the noncircular part at aspecified axial position, and a picture of an outline of the noncircularpart cut along a reference longitudinal line in the picture of the crosssection, placed beside the picture of the cross section, wherein theaxial position of the cross section can be specified.
 18. The machiningdata generator according to claim 7, wherein the graphic display unithas a correcting unit that corrects the graphically displayednoncircular part shape data on a graphic display screen.
 19. Themachining data generator according to claim 7, wherein the graphicdisplay unit has a tolerance data display unit that graphically displaystolerance data on tolerances for the noncircular part shape datatogether with the noncircular part shape data.
 20. The machining datagenerator according to claim 8, wherein the graphic display unit has atolerance data display unit that graphically displays tolerance data ontolerances for the noncircular part shape data together with thenoncircular part shape data.